Structural constants of selected early-type binaries and their astrophysical implications

Abstract

Theoretical values of the structural coefficient k2, have been calculated in dependance on mass and age. The results are relatively more accurately tested from observations of apsidal motion in young and massive binariy systems. For this context, values of k2 were also derived for eleven well-studied and observed eccentric eclipsing–binaries: CW Cep, V 478 Cyg, AG Per, V 453 Cyg, V 578 Mon, PV Cas, V 451 Oph, V 380 Cyg, IQ Per, HD 152,218 and NO Pup. Our new k2 values are calculated by integrating the Clairaut–Radau equation numerically using the ‘EZ-Web’ version of the Eggleton stellar modeling program. Models are in the range between 2.6 and 17.5 Mʘ, constructed with the two metallicities Z = 0.015 and Z = 0.02. From the observations, we obtained a linear regression formula relating system-mean k2 values for given logarithmic mass and age. This correlation can be used to test the match between apsidal motion results and the separately derived ages of the components of a binary system. From these findings, we conclude that empirically determined k2 values have better determined from young and massive binaries than binaries in general. Apsidal motion constants, when calculated from reliable data, can be used to test the ages of the stars. These checks can be made with our correlation for the system NO Pup, which is the subject of current studies.